inimitable

Something that is inimitable is, literally, not able to be imitated. In actual usage the word describes things so uniquely extraordinary as to not be copied or equaled, which is why you often hear it used to praise outstanding talents or performances. (The antonym "imitable" describes things that are common or ordinary and could easily be replicated or surpassed.) Inimitable derives via Middle English from Latin inimitabilis. Be careful not to confuse it with "inimical" or "inimicable," two adjectives meaning hostile or harmful; those words derive from the same Latin root that gave us "enemy" ("inimicus").